1. Field of the Invention
The invention relates to varistors and more particularly to varistors having high energy absorption.
2. Summary of the Prior Art
A wide variety of varistors are known in the prior art. The prior art clearly indicates a continuing effort to improve the energy absorption of varistor discs. High performance prior art varistors frequently utilize Bi.sub.2 O.sub.3 in concentrations higher than 1.0 mole percent. This is a strategic and expensive material thus adding significantly to the cost of the varistors. Varistors having improved high temperature stability and using lower concentration of this expensive material are desirable.
A prior art patent search was performed prior to preparing this patent application. The prior art cited during this search is discussed below.
U.S. Pat. No. 4,724,416, discloses a varistor which includes Bi.sub.2 O.sub.3 in combination with other elements. A varistor including 5 to 30 weight percent of B.sub.2 O.sub.3 and 70 to 95 weight percent SiO.sub.2 is disclosed in U.S. Pat. No. 4,551,268. U.S. Pat. No. 4,527,146, discloses a varistor including bismuth, cobalt, manganese, antimony and nickel. Varistors including a variety of rare earth elements are illustrated in U.S. Pat. No. 4,160,748.
The use of GeO.sub.2 and Bi.sub.2 O.sub.3 is illustrated in U.S. Pat. No. 3,953,373. A method for making varistor discs is disclosed in U.S. Pat. No. 3,905,006. U.S. Pat. No. 3,689,863, discloses a varistor having up to 10 mole percent BeO. Varistors having up to 50 mole percent SiO.sub.2 are disclosed by U.S. Pat. No. 3,872,582. U.S. Pat. No. 4,460,494, discloses a varistor using Cr,Si and SiO.sub.2.
The above patents illustrate the wide variety of mixtures and processes used to form prior art varistor discs. These patents are also believed to illustrate the absence of any unified theory to predict the performance of specific varistors. That is, each new mixture must be experimentally verified in order to predict its performance.